1. Field of the Invention
The present invention relates generally to a novel antenna system for airborne radar warning systems and other applications. More particularly, the present invention relates to a spiral-helix antenna having an expanded bandwidth covering from about 0.5 GHz to about 18 GHz.
2. Description of the Prior Art
Over the years electronic warfare equipment in general and radar warning systems in particular have been characterized by steadily increasing bandwidths and ever expanding frequency limits. For example, early radar warning systems were typically designed to cover only limited sectors of the 2 to 10 GHz band, while present state-of-the-art systems commonly cover the entire range of from 2 to 18 GHz.
More recently, significant interest has been focused on further expanding the bandwidth capabilities of present day systems by providing coverage over an even lower range of the RF spectrum, and, in particular, over the 0.5 to 2 GHz range. One proposal to accomplish this envisions providing a supplementary antenna system to be added-on to existing systems. Such a supplementary system, however, is not particularly desirable because it would require an additional antenna array together with microwave components, higher cost, and increased aerodynamic drag. A much more desirable solution would be to provide a single antenna to cover the entire expanded frequency range. Furthermore, it is important that such an antenna system have substantially the same physical dimensions as standard cavity-backed spiral antennas typically used in airborne radar warning systems. This is important because favorable mounting locations on aircraft are difficult to find and antenna designers have been required to provide broad band performance within a closely defined volume.